1. Field of the Invention
A surface treated, electrolytic copper foil, method for making the foil, and method for wireless charging of Flexible Printed Circuit Board (hereinafter “FPCB”) are disclosed. Numerous types of devices are disclosed where such FPCB can be incorporated and wirelessly charged.
2. Description of Related Art
Many electrical devices currently contain printed circuit boards, being operated by a battery source of electrical power, including secondary batteries as the source of such electrical power. In order to recharge the secondary batteries, the device incorporating the secondary batteries includes a mechanical connector, e.g., a plug or a charging port whereby a source of charging current is connected to the plug or port. The connection heretofore was a wire, with a compatible plug, or alternatively, a docking device into which the charging port is mated.
On the other hand, recent developments have made it desirable to wirelessly charge a secondary battery(s) by transmitting an electrical current from a power source to a receiving device without the use of a physical connection. The electrical current is then used to charge, or re-charge, the battery(s) of the receiving device. In this circumstance, the receiving device can be anything from a smartphone or a wearable to a large industrial forklift.
The concept of wireless charging can be understood as power can be transferred safely over an air gap and also through any non-metal object which might exist between the coil of the transmitter circuit and the coil of a receiver circuit. Examples of such non-metal objects can be wood, plastic, granite, ceramic, glass, etc. The mains voltage is converted into high frequency alternating current (AC) in the transmitting device and is send to a transmitter coil by the transmitter circuit. Alternating current flowing within the transmitter coil creates a magnetic field which extends to a receiver coil in the receiving device (when such transmitter coil and receiver coil are within a specified distance). The magnetic field generates current within the receiver coil of the receiving device, and such current flowing within the receiver coil is converted into direct current (DC) by the receiver circuit, thus charging the battery(s) of the receiving device.
Wireless charging is based on the principle of magnetic resonance or inductive power transfer (hereinafter “IPT”)—a process whereby electricity is transferred between two objects through coils.
In inductive charging, the receiving device is placed directly onto a charging surface and requires precise overlap of the transmitting and receiver coils as illustrated in FIG. 1A. This means that the receiver and transmitter must be closely aligned and the distance between the receiver and transmitter coils is limited to a few millimeters. The advantage of these tightly coupled systems is a higher efficiency compared to magnetic resonant charging.
In magnetic resonance charging (illustrated in FIG. 1B), multiple devices can be charged simultaneously and the magnetic field can be picked up from different areas by the receiving coils of multiple receiving devices. The obvious benefits of magnetic resonance charging are a larger charging area and ability to simultaneously charge multiple devices. The challenges of a magnetic resonant charging solution are the increased EMI (Electro-Magnetic Interference) and a lower efficiency compared to inductive charging.
The benefits of wireless chargers are numerous:                1. Greater convenience and ubiquity for charging of everyday devices;        2. Reduce costs associated with maintain mechanical connectors;        3. Safe powering or charging devices that need to remain sterile or hermetically sealed (waterproof);        4. Prevention of corrosion due to elements such as oxygen or water on the mechanical connections and/or charging port;        5. Elimination of sparks and debris associated with wired contacts;        6. No wire;        7. No need to carry a charger or spare batteries; and        8. Wireless charging eliminates the need for cords, connectors and electrical plugs and allows any user with a compatible device to use the same wireless charging pad.        
Wound copper wire coils are currently used in wireless charging pads as the transmitter coil. They offer lower internal DC resistance, higher quality, higher efficiency, but they have greater thicknesses making it difficult to incorporate in wearables or smartphones and are more costly.
On the other hand FPCB coils can be used in a cellphone as a receiving coil, but have higher internal DC resistance, lower quality, lower efficiency, but are lower thickness and lower cost than wound copper wire coils.
Attempts have been made to produce copper clad laminates employing thin and thick copper foils as found in CN 204526301 U published 5 Aug. 2015. Other attempts to treat copper foil for copper-clad laminated board to provide high peeling strength of the copper with a resin substrate are disclosed in JP 2011219790 (A) on 4 Nov. 2011. Still further, attempts have been made to produce an electrolytic copper foil to satisfy the arithmetical mean deviation from the mean line of the profile Ra in S. Korean examined patent publication 1014493420000, published 13 Oct. 2014. Other attempts at producing copper foils are disclosed in JP Patent 4833692 B2, granted 30 Sep. 2011; and JP Patent 4833556 B2, also granted 30 Sep. 2011. None of these attempts satisfy the requirements of the disclosed embodiments.
Thus, there exists a need for improved copper foils that can be employed as FPCB coils for smartphones, wearables and other articles that do not have the drawbacks of current FPCB coils.